Analysis of rice panicle structure

The IR cultivars and Rewa type (PAU125-1-2/Lalco 14) have similar panicle structure. However, Rewa type has more spikelets on the secondary branches (SB) than do IR cultivars. Glaberrima type has more primary branches (PB) and spikelets on (PB), with few SB and spikelets. The upland type derived from an anther-cultured Moroberekan/Palawan cross is intermediate. The upland type has almost the same number of spikelets on PB (SpPB) and SB (SpSB). PB-SB and SpPB-SpSB ratios were high for the glaberrima type and low for the Rewa type. Total spikelet number in Rewa 353-3/IR47705-AC4 was 278, compared to about 150 spikelets in IR entries. Number of PB was 17.3 in IR47705-AC5/Ch IR87-3-1 and 16.1 in Acc. 103995/IR47705-AC4; the IR varieties had about 10 PB. In crosses with glaberrima or upland type as the female parent, SpSB was 100 or more; the IR varieties had 45-68 SpPB. Heterosis (over midparent), heterobeltiosis (over better parent), and standard heterosis (over IR36) were estimated for PB, SB, SpPB, SpSb and total spikelets (TSp). Estimates of overall degree and direction of heterosis (Fmac1-Pmac) were significant and position for all characters, indicating dominance of higher values. The values for individual F1 families, however, differed from the overall estimates for heterosis in different characters. The F1 means deviated conspicuously from the respective parental and midparental values, indicating nonadditive gene action for most characters. Substantial heterosis in the desirable direction showed in characters like number of PB, SpPB, and TSp, which are related to higher grain yield potential. Most crosses exhibited positive heterosis, heterobeltiosis, and standard heterosis for number of PB and SpPB; however, one Rewa cross, one upland cross, and three glaberrima crosses had negative heterobeltiosis, perhaps because of the already high number of PB and SpPB in the glaberrima parents. Two Rewa crosses (Rewa 353-3/IR47705-AC4 and Rewa 353-2/IR30) and three upland crosses (all but IR47705-AC5-1/IR28211-43-1-1-2) manifest positive heterosis, heterobeltiosis, and standard heterosis for all characters